此试题出现在
Questions 21 to 25 are based on the following passage. Lead deposits, which accumulated in soil and snow during the 1960’s and 70’s, were primarily the result of leaded gasoline emissions originating in the United States. In the twenty years that the Clean Air Act has mandated unleaded gas use in the United States, the lead accumulation worldwide has decreased significantly. A study published recently in the journal Nature shows that air-borne leaded gas emissions from the United States were the leading contributor to the high concentration of lead in the snow in Greenland. The new study is a result of the continued research led by Dr. Charles Boutron, an expert on the impact of heavy metals on the environment at the National Center for Scientific Research in France. A study by Dr. Boutron published in 1991 showed that lead levels in arctic (北极的) snow were declining. In his new study, Dr. Boutron found the ratios of the different forms of lead in the leaded gasoline used in the United States were different from the ratios of European, Asian and Canadian gasolines and thus enabled scientists to differentiate (区分) the lead sources. The dominant lead ratio found in Greenland snow matched that found in gasoline from the United States. In a study published in the journal Ambio, scientists found that lead levels in soil in the Northeastern United States had decreased markedly since the introduction of unleaded gasoline. Many scientists had believed that the lead would stay in soil and snow for a longer period. The authors of the Ambio study examined samples of the upper layers of soil taken from the same sites of 30 forest floors in New England, New York and Pennsylvania in 1980 and in 1990. The forest environment processed and redistributed the lead faster than the scientists had expected. Scientists say both studies demonstrate that certain parts of the ecosystem (生态系统) respond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute. How did scientists discover the source of lead pollution in Greenland? （）
保安服务可以借助安全技术防范系统的（）能力，及时发现不法入侵。
“没有民主就没有社会主义”这句话的意思不包含（）。
聚合物的分子量（）
关于盗窃罪，下列哪些说法是正确的（A、B、D选项不考虑数额）（）
某甲在医学院获得了专科毕业证书，此时他可以（）
某公司工程开始后，工程监理人由于某原因请假三天，在此期间，此公司不可（）
明显的脂肪浸润多见于（）
眼眶T2加权扫描加脂肪抑制技术的原因是（ ）。
男，40岁，晚餐后5小时开始上腹疼痛，向左肩、腰、背部放射及恶心、呕吐、腹胀。现已37个小时。曾有胆结石史。体检：呼吸24次／分，体温38.9℃，血压90/75mmHg。巩膜可疑黄染，全腹压痛，以上腹部显著，伴肌紧张和反跳痛，移动性浊音阳性，血白细胞16×109/L，中性粒细胞89%。为确定诊断，最有价值的检查是（）
暂无相关推荐~
三等及其以上的集中联锁的车站调车进路原则上应一次排列，遇调车进路未排列到（）等股道时，车站值班员（信号员）应在排列进路前预告司机停车位置（用语为“×号机车，过×...
三等及其以上的集中联锁的车站调车进路原则上应一次排列，遇调车进路未排列到到发线、调车线、牵出线、机待线等股道时，车站值班员（信号员）应在排列进路前预告司机停车位...
三等及其以上的集中联锁的车站调车进路原则上应一次排列，遇调车进路未排列到到发线、调车线、牵出线、机待线等股道时，车站值班员（信号员）应在排列进路前预告司机停车位...
三等及其以上集中联锁的车站每钩调车作业必须执行“问路式”调车规定。
三等及其以上的集中联锁的车站调车进路原则上应一次排列，遇调车进路未排列到（）等股道时，车站值班员（信号员）应在排列进路前预告司机停车位置（用语为“×号机车，过×...
三等及其以上集中联锁的车站每钩调车作业必须执行“问路式”调车规定。
车站联锁
车站联锁
车站联锁
非集中联锁站一般为（）的车站。